The invention relates generally to escalators and, in particular, to an apparatus for the initiation of the shut down of an endless step conveyor belt.
Typically, endless step conveyor belt type escalators consist of a plurality of steps attached between two endlessly circulating flat link chains and guided between two balustrade skirtings. The steps form a lead, which can be stepped down, and a return. The lead has upper and lower horizontal runs, an inclined run and two transition arches which connect opposite ends of the inclined run with the horizontal runs.
For reasons for safety, every escalator has a number of monitoring and shutoff devices, many of which are required to comply with the local safety regulations. For example, the return movement of an upwardly moving escalator has to be prevented, or a downwardly moving escalator must not exceed the normal velocity by more than 20% and has to be stopped automatically on reaching excess velocity. Likewise, an escalator has to be switched off if a step lowers such that the tread of the step cannot, for some reason, be guided any longer in a satisfactory manner through a fixed gate.
Such a device for the shutoff of an escalator is shown in the German Pat. No. DE 628 503. When the escalator velocity exceeds the normal velocity by about 20%, shutdown is initiated. The movement of the step conveyor belt is by a direct current motor, which drives the main shaft by way of a speed reduction drive and a chain drive. A regulator operating by the centrifugal force system is driven by a chain from the main shaft and monitors the escalator travel velocity. An electromagnet in the regulator adjusts a regulating sleeve of a velocity controller corresponding to the chosen normal travel velocity, so that the controller will only respond at two selected travel velocities and stop the escalator when a predetermined excess velocity is reached. For the selection of the velocity and direction of travel, a selector switch for a low and a high velocity and a direction switch are housed in an instrument cabinet.
Another device for the shutoff of escalators is shown in the German Patent Application No. DE 33 19 831. A shutoff apparatus switching means is operable by the lowering of a step of the escalator. The switching means includes a spring-suspended supported copper wire insulated with respect to the supporting structure of the conveying installation. One pole of a direct current source is connected to the copper wire, and the other pole is connected to the supporting structure of the conveying installation. As soon as a tread body is lowered, for example, when the rubber tire of a running roller of a tread body loaded by at least one passenger drops off, the step body contacts the copper wire and closes the circuit of the direct current source. The drive of the conveying belt is then switched off by a relay.
A further device for the shutoff of an escalator is shown in the European Pat. No. 082 074, in which, with the aid of at least a distance sensor positioned in the return of the step conveyor, every single step is monitored by a logic circuit. At the absence of a step, the logic circuit generates an error signal on command of the distance sensor and causes the immediate stop of the escalator by way of a relay.
Another device for the shutoff of an escalator is shown in the U.S. Pat. No. 4,151,381. The escalator is stopped automatically as soon as the step conveyor moving for upward travel starts to move unintentionally to a downward direction. An idler roll driven by the main drive shaft of the drive has a peripheral groove which is in frictional connection with an operating rod. The rod rests in the peripheral groove and is axially slidingly supported, and interacts with a switching lever of a limit switch. With an upward moving step conveyor, the idler roll is driven counterclockwise, where the operating rod is pulled away by friction from the switching lever of the limit switch and abuts a detent plate. If the step conveyor reverses, the operating rod is pushed by the friction of the clockwise moving idler roll against the switching lever of the limit switch, whereby the limit switch is operated and the escalator is stopped.
All the above described devices for the shutoff of an escalator have the drawback that a separate apparatus is required for each individual monitoring task, and that each monitoring apparatus is relatively expensive.